This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Successive to continuing comparative investigations regarding the characterization of Pseudomonas aeruginosa (ATCC 27853) cultured in hyperbaric environments, this study will examine the reduction rate changes and residual accumulations induced as P. aeruginosa switches from aerobic to anaerobic denitrification under normobaric and hyperbaric conditions. Results of preliminary aerobic normobaric and hyperbaric denitrification studies distinguish contrasting commencement delays, reduction rates and residual accumulations, suggesting that P. aeruginosa may select alternative oxidation-reduction systems in the transition between normoxic and hyperoxic conditions. Of particular interest to this study, will be the increased cell-cell adhesion phenomenon (biofilm or biofilm-like formation) that has been observed in previous hyperbaric studies. This increased cell association, at the atmosphere-media interface, has the propensity to produce microenvironments that could differ dramatically in composition, thereby significantly affecting the aforementioned characteristics of denitrification. Results from these studies may have relevance to issues surrounding Pseudomonas spp. involvement in the epidemiology, pathology and chemotherapy of external and middle ear infections of personnel living in extreme environments (i.e., submarines, space stations and undersea habitats), synergetic chemotherapeutic and hyperbaric oxygen treatment of severe burn victims, and multi-staged nitrate bioremediation processes.